1. Field of the Invention
This invention relates to a sampling system for collecting a sample in a sample cylinder having valves on both ends. More particularly, this system provides a loop including sample cylinder connections and a level indicator. In use, a sample cylinder is placed in the connections and the fluid is allowed to flow through the loop until the loop is liquid-filled and contains a representative sample. Then, the flow is diverted from the loop. Fluid is removed from the loop to lower the pressure in the loop, thus vaporizing the liquid. This continues until a vapor-liquid interface is obtained in the sample cylinder as indicated by the level indicator. When this occurs, the valves at both ends of the sample cylinder are closed to isolate the sample contained in the sample cylinder.
2. Description of the Related Art
In the operation of many chemical and other processes, it is often necessary to periodically sample fluids which are flowing within the process at various points. For a variety of reasons, it is often advantageous to collect the fluid in a sample cylinder having valves on both ends. A sample cylinder having valves on both ends is particularly applicable for obtaining samples of liquids having high vapor pressure. Hydrocarbon liquid samples, e.g., LPG (liquified petroleum gas) and butane, are frequently caught in sample cylinders having valves on both ends.
When collecting a liquid sample in a sample cylinder having valves on both ends, it is known to vent the cylinder to provide a vapor space in the cylinder to prevent rupture due to liquid expansion in a liquid filled cylinder, e.g., upon an increase in temperature.
The known systems and methods for collecting a sample in a sample cylinder having valves on both ends presents several disadvantages. First, many known systems and methods require excessive venting of sample material to the atmosphere to achieve a representative sample in the sample cylinder and/or to achieve a vapor space in the sample cylinder. This venting of sample material results in health concerns in that the person catching the sample is exposed to the sample material and environmental concerns due to contamination of the air, and in some cases, the soil or water runoff. Also, known systems for the collection of a sample in a sample cylinder having valves on both ends typically require the operation of several valves. This may lead to errors in collecting a representative sample and is time consuming as it requires special procedures.
U.S. Pat. No. 4,712,434 to Herwig discloses a sample system for capturing a sample in a sample cylinder having valves on both ends. The system includes a 4-way tap from which leads two lines, which can be connected together from and to the sample source and to other lines which can be connected together which lead to a sample cylinder having valves on both ends. The system further includes a supply line for an inert gaseous flushing medium which joins the line leading into the sample cylinder, and a discharge line for the inert flushing medium, which leads from the line coming out of the sample cylinder and proceeds to a disposal system. In use, the system and sample cylinder are first flushed with an inert gaseous flushing medium with the flushing medium being routed to the discharge line and disposal system. Then, a predetermined volume of the inert gaseous flushing medium is captured between two valves in the discharge line. Next, the four-way tap is positioned to allow the sample to flow through the system and sample cylinder. Then, the four-way tap is positioned so as to isolate the sample cylinder. Next, the valve in the discharge line closest to the sample cylinder is opened to allow the inert gaseous flushing medium to enter into the system and sample cylinder so as to provide a vapor space in the sample cylinder.
There are several disadvantages to the system and method disclosed in U.S. Pat. No. 4,712,434 to Herwig. First, the system must be flushed with the inert gaseous medium prior to collecting the sample in the sample cylinder. This flushing is disadvantageous for several reasons. As it includes several steps, it may take considerable time to flush the system and collect the sample. Also, due to the required number of steps, it may lead to operator error which may result in accidental release of sample or inert gaseous flushing medium. Also, due to the volume of flushing material, the system may be costly to operate or require special disposal facilities. Second, by using an inert gaseous flushing medium to obtain the vapor space in the sample cylinder, the sample cylinder may become "contaminated" with the inert gaseous flushing medium. This presents a problem, especially for LPG sampling, because the level of "inerts" within a production sample is an important measurement, as an increased level of inerts present may subsequently raise the pressure of storage facilities, resulting in venting of the storage facilities or over-pressuring the storage facilities. Third, this system is difficult to operate in that the technician (person collecting sample) cannot easily determine whether the system is operating correctly. This may lead to the collection of a non-representative sample or the sending of excessive sample and vent material to the disposal system.
U.S. Pat. No. 5,131,282 to Kuhner discloses a system for collecting a sample in a sample cylinder having valves on both ends, the system having two three-way valves, with each valve of the sample cylinder being connected to a three-way valve. Here, each three-way valve has three positions, i.e., a sample position, a vent position, and an off position. With this number of operating variables, the system is complicated and requires several steps to operate. This could lead to operator error in relation to collecting a representative sample or accidentally releasing material to the atmosphere which may result in health or environmental concerns. Also, this system does not provide a satisfactory means for obtaining a vapor space in the sample cylinder without venting the sample cylinder to the atmosphere.
Thus, there exists a need for a sampling system for collecting a sample in a sample cylinder having valves on both ends which allows quick, easy, and uncomplicated collection of the sample, and which allows a technician to easily and accurately determine that the system is operating correctly.